Noncontacting keyboard

ABSTRACT

An array of keys is suspended over an array of transformers. The transformer secondaries are series connected together and the primaries are arranged in series connected pairs, the transformers of each pair being oppositely poled. A ferrite core is attached to each key. The primary pairs are electrically energized one at a time by a scanner, and the series connected secondaries are connected to a comparator. When a key is depressed the ferrite core on the key changes the mutual inductance between the primary and secondary of the corresponding transformer, causing the comparator to register a depressed key. An information output available from the scanner and comparator tells which key is depressed, and the scanner halts when a key is depressed to prevent an erroneous output due to more than one simultaneously depressed key.

United States Patent Cochran et al. 1 June 6, 1972 NONCONTACTING KEYBOARD [72] Inventors: David S. Cochran, Palo Alto; Glenn E. Primary Examiner john w'caldwen McGhee, Los Altos, both of Calif.

GENERATOR 'll/III:

' PULSE 18 2'20 Assistant ExaminerRobert J. Mooney Attorney-Roland l. Griffin ABSTRACT An array of keys is suspended over an array of transformers. The transformer secondaries are series connected together and the primaries are arranged in series connected pairs, the transfonners of each pair being oppositely poled. A ferrite core is attached to each key. The primary pairs are electrically energized one at a time by a scanner, and the series connected secondaries are connected to a comparator. When a key is depressed the ferrite core on the key changes the mutual inductance between the primary and secondary of the corresponding transformer, causing the comparator to register a depressed key.v An information output available from the scanner and comparator tells which key is depressed, and the scanner halts when a key is depressed to prevent an erroneous output due to more than one simultaneously depressed key.

9 Claims, 6 Drawing figures PATENTEDJUH 6 I972 3, 668 697 SHEET 2 OF 4 INVENTOR.

DAVID S. COCH'RAN GLENN E. MC GHEE PATENTEUJUH s 1972 SHEET 4 0F 4 GLENN E MC GHEE N ONCONTACTING KEYBOARD BACKGROUND AND SUMMARY OF THE INVENTION In the prior art keyboards for use with computers, calculators, data terminals and the like usually had an array of mechanical switches, one for each key on the keyboard, which were connected to encoding electronics for generating a digital code corresponding to the key. Limitations of such keyboards include wear and corrosion of the switch contacts, erroneous code generation due to contact bounce, high mechanical and electrical complexity, and corresponding high cost and low reliability.

In a preferred embodiment of the present invention the keyboard is comprised of an array of printed circuit transformers with a key or button for each transformer. All of the transformer secondaries are connected together in series and the series combination is connected to comparator amplifiers. The transformer primaries are grouped in series connected pairs and the pairs are sequentially energized by a scanner. The transformers in any one pair are oppositely poled. The polarity of a transformer is determined by the phase of a signal at the transformers secondary compared with the phase at its primary. Depending upon the sense of the primary and secondary windings, and therefore the polarity of the mutual inductance, the phase of a signal may be either unaltered or inverted by a transformer. Since each pair of transformers is oppositely poled and the transformers are otherwise identical, the signals on the series connected secondaries normally cancel. Each key has a magnetic flux changing element such as a ferrite rod or core on it, and when a key is depressed, the ferrite element is brought closer to the transformer. The mutual inductance between the primary and secondary of the transformer is changed (in this example increased) by the presence of the ferrite, and the previously mentioned cancellation is upset, producing a signal at the comparator. The polarity of the signal tells which transformer of the pair was actuated, and the scanner tells which pair was energized when a signal appeared at the comparator. An interlock is provided to stop the scanner when a key is depressed to prevent the detection of more than one depressed key at a time. The entire keyboard is scanned in a few milliseconds so, to human perception, the response to a depressed key is instantaneous. Thus, a keyboard is realized which does not require the mechanical closure of contacts.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows one pair of keys of a noncontacting keyboard.

FIG. 2 shows a preferred physical configuration of the keys and keyboard.

FIGS. 3-6 show different simplified embodiments of a noncontacting keyboard according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a pair 11 of key assemblies and 12. A primary winding 18 of key assembly 12 is connected in series with a primary 14 of key assembly 10 and pulse generator 28. A pulse 42 from generator 28 is applied to primaries 14 and 18, and pulses 44 and 46 appear on secondaries l6 and 20, respectively. The dots near the transformer windings indicate the polarity of the windings, and it can be seen that pulse 46 is inverted with respect to pulse 42 while 44 is not inverted. Since the mutual inductance in the transformers is designed to be the same, pulses 44 and 46 are of the same magnitude, but of opposite phase or polarity, so they cancel. Key assemblies 10 and 12 also include keys 22 and 24, respectively, and each key includes a magnetic flux changing element 26. Element 26 may take a number of forms. To increase the mutual inductance between the primary and secondary, a magnetic material such as ferrite may be attached to the key. The ferrite may be in the shape of a rod or core which moves near the windings when the key is depressed. Alternatively, a piece of metal can be used for element 26 to decrease the mutual inductance between the primary and secondary, the piece of metal acting essentially as a shorted turn. The metal, brass, for example, could be in the shape of a disc or washer which almost contacts the transformer coils when the key is depressed. A simple suspension system for keys 22 and 24 might comprise, for example, a hole in panel 23 through which flux changing element 26 moves, a spring 25 to bias the key in the up" position, and a retainer 27 to limit the travel of the key. Panel 23 might be that of a calculator, data terminal or other device requiring a keyboard.

If key 24 is depressed, as indicated by arrow 40, pulse 46 will increase in magnitude, assuming for the sake of example that element 26 is fem'te. Pulses 44 and 46 will no longer cancel and a signal will appear at the input of comparator 48. Comparator 48 comprises input resistors 34, amplifiers 30 and 32, and flip-flop 36 which stores the output of amplifiers 30 and 32. Each of the amplifiers 30 and 32 will pass only a positive polarity pulse. Pulse 44 will be positive to amplifier 30 and will therefore reset flip-flop 36; pulse 46 will be positive to amplifier 32 and will set flip-flop 36. During the time key 24 is depressed, output 38 of flip-flop 36 will be a logical l the code arbitrarily selected for key 24 in this example.

FIG. 2 shows a preferred physical embodiment of a portion of a noncontacting keyboard. Keys 22 and 24 are supported through holes in panel 23 by spring 25. The flux changing element is shown as a metallic disc 126 such as brass or copper attached to each key. A printed circuit board supports printed circuit transformers and 112. Key 24 is shown in the up position with its disc I26 held above transformer 112, while key 22 is shown depressed, as indicated by arrow 41, with its disc 126 in closer proximity to transformer 110. It is not necessary for the disc to touch or pass between the windings.

FIG. 3 shows a simplified keyboard with eight pairs 11 of key assemblies. The pairs of primaries are connected in parallel to pulse generator output bus 66. Each primary pair is also tied to terminals 49 of a counter 50. Counter 50, shown as a scale of eight counter, sequentially connects one terminal 49 to ground each time it receives a pulse from generator 28 through delay 54 and AND gate 52. Thus, for each pulse 42 from generator 28, a different key assembly 11 is pulsed. Either amplifier 30 or 32 will have an output when a key is depressed and that signal, coupled to AND gate 52 through OR gate 56 and inverter 57, will halt counter 50 by turning off AND gate 52. Delay 54 prevents counter 50 from being stepped before comparator 48 can check for a depressed key. Thus, elements 52, 54, 56, and 57 serve as a lockout circuit to prevent an output in response to more than one depressed key. Key code information is available to external equipment on output 58, comprising three outputs from counter 50 and output 38 from flip-flop 36. A key down" signal is also provided on output 62. In this example, counter 50, delay 54, and gates 52 and S6 in conjunction with pulse generator 28 comprise a scanner.

One method of expanding the noncontacting keyboard is shown in FIG. 4. In this embodiment primary groups 64 of four primaries connected in series are shown with half of the secondaries series connected to comparator 68 and the other half to comparator 70. As in FIG. 3, the primary groups 64 are pulsed sequentially by generator 28 and counter 50; the remaining circuitry has been abbreviated or omitted for clarity.

Another method of scanning the primaries in a noncontacting keyboard is illustrated in FIG. 5. Sixteen keys are illustrated as in FIG. 3, but the counter is only a scale of four counter rather than a scale of eight counter. Alternate pairs 11 of primaries are connected to an output 74 of a flip-flop 80 and the other pairs 11 are connected to a second output 76. The generator 28 drives flip-flop 80, and therefore outputs 74 and 76 are alternately energized. Diodes 75 ensure that current flows in only one of the lines connected to outputs 74 and 76. Adjacent pairs of primaries are connected to one of the four terminals on counter 51, and counter 51 is driven by flipflop 80 rather than directly by generator 28. Thus, counter 51 grounds a different set of primaries after two pulses from generator 28. Output 78 comes from counter 51, flip-flop 80 and comparator 48. This method of scanning is known as X-Y scanning.

FIG. 6 illustrates an alternative embodiment of a lockout circuit from that shown in FIG. 3. For the sake of simplicity, only eight keys are shown in this example. Output 58 is connected to a buffer store 90 which enters a new key code into memory every time there is a key down pulse on line 94. Thus the information available on buffer store output lines 96 represents the key depressed during a given cycle n of counter 50. The information on output 58 represents the key depressed during cycle n+1 of counter 50. The information on outputs 58 and 96 are compared in a digital comparator 92; if they coincide, a key down signal appears on an output 63. Thus a key down signal will appear on output 63 only if the same key is depressed for two or more cycles of counter 50. Key code information appears on output 59.

The keyboard illustrated in FIG. 4 can be expanded either by increasing the number of input lines to counter 50 or the number of pairs of primaries connected in series and thus the number of comparators. The keyboard of FIG. 5 can be expanded either by increasing the number of input lines to counter 51 or the number of flip-flops 80 driven by pulse generator 28. Scanning methods other than those illustrated are also possible; for example, all primaries could be connected in series and pairs of secondaries could be connected to an array of comparators.

We claim: 1. A noncontacting keyboard comprising: an array of coreless transformers, each transformer having a first and a corresponding second winding, the first windings being series connected in one or more first groups and the second windings being series connected in one or more second groups, each first group containing an integral number of pairs of the first windings, and there being at least said integral number of second groups;

energizing means connected to the first groups for applying signals thereto, the magnitude and polarity of the mutual inductance between the pairs of first windings in a first group and the corresponding second windings being selected for cancellation of signals induced on said corresponding second windings in response to signals on the first windings;

an array of buttons arranged in a one to one correspondence with and physically proximate to the array of transformers, a pair of buttons corresponding to a pair of first windings and said buttons being supported for movement with respect to the transformers; magnetic flux changing means attached to each button for changing the mutual inductance between the first and second windings in one of the transformers when the button corresponding to that transformer is moved to change the proximity of the magnetic flux changing means with respect to the transformer; and v circuit means connected to the second groups for giving an electrical indication of which button was moved, said circuit means including comparator circuitry for determining the polarity of a signal caused by the change in mutual inductance between the first and second windings of a transformer to identify which button in a pair buttons was moved and logic means responsive to the comparator circuitry for storing a digital indication of the polarity of the change in mutual inductance.

2. A noncontacting keyboard as in claim 1 wherein the energizing means includes a signal source and scanning means for connecting one of said integral number of pairs of the first windings at a time to the signal source.

3. A noncontacting keyboard as in claim 2 wherein the circuit means includes latching circuitry to halt the scanning means when the circuit means gives an electrical indication that a button was moved.

4. A noncontacting keyboard as in claim 2 wherein the magnetic flux changing means is a piece of ferrimag rietic material. 5. A noncontacting keyboard as in claim 2 w erein the magnetic flux changing means is a piece of metal.

6. A noncontacting keyboard as in claim 2 wherein said integral number is one.

7. A noncontacting keyboard as in claim 2 wherein the circuit means includes digital coding means responsive to the comparator circuitry and the scanning means, the digital coding means giving a digital output corresponding to the button moved.

8. A noncontacting keyboard as in claim 7 including latching means for comparing the digital output corresponding to successive scans of the scanning means, the latching means giving an output in response to the same button being moved during at least two successive scans.

9. A noncontacting keyboard as in claim 5 wherein the transformers are metal foil spirals on a printed circuit board, the buttons are supported above the printed circuit board by spring means, and a button is actuated by depressing it, bringing said piece of metal in closer proximity to the correspond- I ing transformer. 

1. A noncontacting keyboard comprising: an array of coreless transformers, each transformer having a first and a corresponding second winding, the first windings being series connected in one or more first groups and the second windings being series connected in one or more second groups, each first group containing an integral number of pairs of the first windings, and there being at least said integral number of second groups; energizing means connected to the first groups for applying signals thereto, the magnitude and polarity of the mutual inductance between the pairs of first windings in a first group and the corresponding second windings being selected for cancellatioN of signals induced on said corresponding second windings in response to signals on the first windings; an array of buttons arranged in a one to one correspondence with and physically proximate to the array of transformers, a pair of buttons corresponding to a pair of first windings and said buttons being supported for movement with respect to the transformers; magnetic flux changing means attached to each button for changing the mutual inductance between the first and second windings in one of the transformers when the button corresponding to that transformer is moved to change the proximity of the magnetic flux changing means with respect to the transformer; and circuit means connected to the second groups for giving an electrical indication of which button was moved, said circuit means including comparator circuitry for determining the polarity of a signal caused by the change in mutual inductance between the first and second windings of a transformer to identify which button in a pair buttons was moved and logic means responsive to the comparator circuitry for storing a digital indication of the polarity of the change in mutual inductance.
 2. A noncontacting keyboard as in claim 1 wherein the energizing means includes a signal source and scanning means for connecting one of said integral number of pairs of the first windings at a time to the signal source.
 3. A noncontacting keyboard as in claim 2 wherein the circuit means includes latching circuitry to halt the scanning means when the circuit means gives an electrical indication that a button was moved.
 4. A noncontacting keyboard as in claim 2 wherein the magnetic flux changing means is a piece of ferrimagnetic material.
 5. A noncontacting keyboard as in claim 2 wherein the magnetic flux changing means is a piece of metal.
 6. A noncontacting keyboard as in claim 2 wherein said integral number is one.
 7. A noncontacting keyboard as in claim 2 wherein the circuit means includes digital coding means responsive to the comparator circuitry and the scanning means, the digital coding means giving a digital output corresponding to the button moved.
 8. A noncontacting keyboard as in claim 7 including latching means for comparing the digital output corresponding to successive scans of the scanning means, the latching means giving an output in response to the same button being moved during at least two successive scans.
 9. A noncontacting keyboard as in claim 5 wherein the transformers are metal foil spirals on a printed circuit board, the buttons are supported above the printed circuit board by spring means, and a button is actuated by depressing it, bringing said piece of metal in closer proximity to the corresponding transformer. 